A couple of weeks ago, Chicago Transit Authority president Forrest Claypool announced that the agency would install high-definition surveillance cameras in 850 rail cars. There are already more than 3,600 cameras throughout the rail system, in stations and on trains, and the CTA spent a lot of money putting them there—approximately $26 million. “With more cameras, we will be able to step up our efforts to fight crime on the system,” said Claypool.

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But the Chicago Sun-Times reports that rail-station crime has actually increased since the cameras were installed. The Sun-Times found that, in 2012, the number of crimes reported at CTA rail stations jumped by 21 percent year over year, and by 32 percent from 2010, prior to when most of the cameras were installed. Many of these crimes involve theft, drug use, vandalism, and fare evasion. (CTA spokesman Brian Steele told me that much of the rise in crime is due to a 41 percent jump in fare evasion.) Violent crime, however, is down by 30 percent, while arrest rates are slightly up.

Given those stats, should we consider the CTA’s camera programa crime-fighting success or a money-wasting failure?

Surveillance cameras aren’t cure-alls—they’re tools, and imperfect ones at that. They can be easily foiled by the latest in apparel technology, including hooded sweatshirts and hats. They tend to break. They are susceptible to dirt, and bad weather, and darkness. And even if a suspect is photographed, he still has to be identified and located, which, for overworked police officers, can be a daunting task. While there are more than a million closed-circuit surveillance cameras in London, a police report found that, in 2008, one crime was solved per 1,000 cameras—an abysmal ratio.

The CTA is following the lead of the Chicago Police Department, which over the last decade has installed over 8,000 surveillance cameras across the city. As a WBEZ-FM story put it last year, “Chicago may be the most heavily surveilled city in the nation.” As someone who has received multiple traffic tickets for allegedly running red lights at surveilled intersections in Chicago (the lights looked yellow to me), I can confirm that these cameras are excellent at punishing minor traffic infractions. But apparently they don’t do much to deter more serious crimes, as evidenced by Chicago’s shockingly high murder rate.

When cameras work, it seems, they succeed as part of a broader strategy. David Bradford, executive director of Northwestern University’s Center for Public Safety, told the Sun-Times that surveillance cameras can be more effective when accompanied by signs that announce the cameras’ presence. The idea is to inform patrons that they’re being watched, stopping crimes before they start. While some signs have been placed in the CTA system, the Sun-Times found that they’re obscured in some stations and missing from others.

It’s also possible, though, that prominent signage might make things worse by creating the false illusion of safety and watchfulness. This February, the Chicago Tribune’s Jon Hilkevitch reported that the cameras aboard CTA trains are not actively monitored by law enforcement. There’s no funding available for live surveillance, so the footage is stored for later downloading and review. (CTA spokesman Brian Steele told me that the on-train cameras can, however, be monitored by the rail operator.) As for the in-station cameras, the Sun-Times reports that they “can be monitored by authorities remotely, in real time.” Steele told me that the decision to do so depends on the day and the situation.

If you’re not smart about monitoring your feeds, then your video surveillance program won’t be effective, no matter how many cameras you’ve placed. A 2011 Urban Institute report on citywide police camera systems studied the cameras’ effect on crime in two separate Chicago neighborhoods. Crime levels fell in one but remained steady in the other, and the report cited local residents who believed that the cameras in the latter neighborhood weren’t being actively monitored by police. Maybe the local residents were right, maybe they weren’t. But it’s still a good rule of thumb: All the cameras in the world won’t make a difference if nobody’s watching.

Bodies are dropping left and right in Chicago—at least 51 murders have been reported since the start of 2013—and the cash-strapped police department is scrambling to prioritize its resources. At the beginning of February, the CPD announced that it would no longer respond immediately to 911 calls for non-violent offenses. This is likely one reason why they’re installing so many cameras—they’re cheaper than actual personnel. “We can't afford to have a police officer on every corner, but cameras are the next best thing,” said then-Mayor Richard M. Daley in 2009. But if they’re not being deployed strategically, the next best thing will never be good enough.

Justin Peters is a writer for Slate. He is working on a book about Aaron Swartz, copyright, and the rise of “free culture.” Email him at justintrevett@fastmail.fm.